Permanent colorimetric standard for hydrogen ion determination



Patented Aug. 19, E924.

UNITED STATES PATENT OFFICE.

MARION S. BADOLLET. JO'HN HAMILTON, AND CHARLES F. WALTON, JR., 0]? WASH- INGTON, DISTRICT OF COLUMBIA, DED ICATED, BY MESNE ASSIGNMENTS, TO THE CITIZENS OF THE UNITED STATES OF AMERICA.

PERMANENT COLORIMETRIC STANDARD FOR HYDROGEN ION DETERMINATION.

No Drawing.

To all whom it may concern: p I

Be'it known that we, MARION BADULLl-l'l, JOHN HAMILTdN, and CHARLES F. WALToN, Jr., citizens of the United States of America, and employees of the United States Department of Agriculture, residing in the city of Washington, District of Columbia, have invented Permanent Colorimetric Standards for Hydrogen Ion Determination. This application is made under the act of March 3, 1883, chapter 143 (22 Stat. 625) andv the invention herein described and claimed may be used by the Government of the United States or any of its officers or employees in the prosecution of work for the Government, or by any citizen of the United -hteatea without payment to us of any royalty reon.

invention relates to the use in colorimetliclrydrogen ion determinations of, improved st'wndards for color comparison.

Various dolorimetric methods have been proposed for measuring hydrogen ion concentration, all ofwhich are associated with certain limitations and disadvantages in actual ractice. Some 0t these methods work airly well on relatively pure and colorless solutions, whereas when it comes to determining the hydrogen ion concentra tion of sugar and other solutions, particu larly when these are highly colored, they do not ive the desired degree of accuracy. Considering the various methods and their limitations, it is considered that the so-called block comparator method is the most accurate in principle, and furthermore that, in

- adds actual practice with highly colored substances, it ives the most satisfactory results. Brie 'y, this method makes use of a series pf color StBJldflIdS'SO prepared for each chemical indicator bv usingyarying amounts of indicator that the characteristic color decreases from one extreme to the other. As an example, choosing bromcresol purple from the various indicators, this material in specified amount has a characteristic urple color when sufiicient alkali is d to producethe full alkaline color. Using'less of the indicator the color is less intense. It is not necessary to add an excess of alkali, as the characteristic color is not further intensified. Similarly, when Applicatio filed March 4, 1924. Serial No. 696,887.

(FILED minim ACT or macs: a, 1883, 22 s'ra'r. 1... 625.

suliicient acid is added to .produce the -full and or yellow color, this, for bromcresol purple, is a characteristic color \ylien. of

course, the indicator is used in the-specified amount, so that this yellow tint corresponds to the other extreme at which the indicator is of value to determine accurately hydrogen ion concentrations. The various other indicators which are used for this purpose behave similarly when specified amounts of indicator are taken and series of liquid color standards prepared therefrom. These indicators, in other words, are dyes which are of one color in acid solution and another color in alkaline medium, the depth of tint depending on the amount of indicator used.

It is possible, therefore, by making use of this underlying principle, to reproduce a number of intermediate colors by the methods of chemistry, and in this way to arrange a series of colors graded from one extreme to the other with mathematical exactness. The color scale can then be divided to show what color for each indies. tor corresponds to a definite hydrogen ion concentration. In making use of this method of analysis, a certain number of drops of indicator of definite stren h are added to a specified volume of the so ution to be tested for acidity, the number of dro s which are used corresponding to the num er of drops used in the color' standard. By simply comparing colors, it is then easi y possible to determine the hydrogen ion concentration.

A more complete description of this method is given in the Journal of the American Chemical Society, volume' 42, 1920, pages The colorimetric method above described has recently been modified as follows: In

while the other has contained the indicator in which the full acid color has been developed. By superimposing the wedges, therefore, and looking through to the light, the graduation of color is the same as though a series of se arate color standards had been prepared. he wedge idea is excellent for the p use, but the use of the indicator in liquid orm within a trans a'rent case has not, in ractioe, roved to e satisfactory. The un erl ing 0 jection to this is the fact that the colhrs are not permanent. Various preservatives have been used to retard mold growth, deterioration by the light, or dc,- terioration throu h the chemical reaction of the indicator itse f with the containin receptacle. It has proved impossible, however, as yet, to so preserve these liquids. that the colors remain permanent.

Our invention consists in the substitution of solid color standards made up to be used either as described for the block comparator method usin separate color standards, or to be used in t e wedge method. Provided it is desired to use the block comparator method, it is recommended to make up a number of individual colors shading gradually when placed together from one extreme to the other. This would be comparatively difficult to do, in that a large amount of experimenting would be necessary to reproduce exactly the desired colors. The method recommended is to make use of the wedge idea, making for each indicator two colored wedges of lass or other transparent material, one of w ich is the full acid color and the other the full alkaline color. The chemicals used to produce the desired colors in the solid material necessarily vary with the indicator colors to be duphcated. The selection of the proper chemicals and the transparent material in which the colors can best be incorporated in solid and permanent form is not claimed as our invention.

In using the wedge com arator method, it is necessary to put the h uid to be examined, and also a sam le 0 the same liquid containing the speci ed amount of indicator, in flat containing vessels. Flat containers give better results than cylindrical containers, for the reason that there is less optical error. The apparatus at present on the market is unsatisfactor for the purpose, inasmuch as it is made 0 transparent material which is somewhat colored; hence an error is introduced in making the determination, this error dependin on the degree of color in the containers which are used. It is recommended that these containers be made of absolutely colorless material, so that no error whatever will be introduced in connection with the analyses.

We claim Permanent colorimetric standards for hydrogen ion determinations made from solid and transparentsrnaterial, and containing permanent colors to correspond with those iven by the use of well-known chemical indicators.

MARION S. BADOLLET. JOHN HAMILTON. CHARLES F.- WALTON. JR. 

